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// run
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import "fmt"
type I interface {
M()
}
type S struct {
str string
}
func (s *S) M() {}
var _ I = &S{}
type CloningMap[K comparable, V any] struct {
inner map[K]V
}
func (cm CloningMap[K, V]) With(key K, value V) CloningMap[K, V] {
result := CloneBad(cm.inner)
result[key] = value
return CloningMap[K, V]{result}
}
func CloneBad[M ~map[K]V, K comparable, V any](m M) M {
r := make(M, len(m))
for k, v := range m {
r[k] = v
}
return r
}
func main() {
s1 := &S{"one"}
s2 := &S{"two"}
m := CloningMap[string, I]{inner: make(map[string]I)}
m = m.With("a", s1)
m = m.With("b", s2)
it, found := m.inner["a"]
if !found {
panic("a not found")
}
if _, ok := it.(*S); !ok {
panic(fmt.Sprintf("got %T want *main.S", it))
}
}